1. Field of the Invention
This invention relates to magnetic recording and reproducing apparatus, and particularly to a magnetic head apparatus for use in high density recording and high efficiency reproduction.
2. Description of the Prior Art
Known types of magnetic head apparatus widely used for magnetic recording and reproducing apparatus, such as video tape recorders or video sheet recorders, include:
(1) A combination system which uses the same magnetic head or heads for both recording and reproducing; and
(2) An individual system which uses separate heads for recording and reproducing.
Recently developed magnetic recording media have a characteristic suited for recordings of high density, for example, a high coercive force to prevent a self-demagnetizing action due to the recording of high density and a rapid decrease in reproducing output. The video sensitivity of a magnetic recording medium adaptable for recording at a high density as noted above is predicted by the following equation, as described in the Collection of Dissertations For 5th Science Lecture On Applied Magnetism (Page 76 to Page 77, 9, 1973),
______________________________________ Video sensitivity = 0.363 Bm* + 0.434 Br* / Bm + (.lambda. = 2.2.mu.) 1.200 Hc* - 0.185 .DELTA.Hc* 1/2 + 0.168 d* + 0.169 REF* + 0.580 ______________________________________
The mark (*) signifies that the values are those for standard tape converted into decibells.
Bm = Maximum magnetic flux density,
Br = Residual magnetic flux density,
Br/Bm = Squareness ratio,
Hc = Coercive force,
.DELTA.Hc/2 = The half width of the differential curve near at its Hc, which relates to the steepness of slope of B - H curve.
REF = The reflected light intensity (45.degree. to 45.degree. ) from the surface of the sample.
D = Thickness of magnetic layer,
.lambda. = Recording wave length.
The video sensitivity, from the above equation, increases at the coercive force becomes high, but the magnetic medium requires an intense recording magnetic field, with the result that saturation of the magnetic flux density of the recording system head cannot be ignored. As a consequence, the actual video sensitivity tends to be lower in value than the predicted value obtained from the equation. For example, FIG. 1 shows the relationship between coercive force of a given magnetic recording medium and the video sensitivity for a recording wave length of 2.2.mu., in which curve A represents the predicted value of sensitivity, curve B represents the actually measured value of sensitivity using an alloy head (Sendust) for recording and reproduction, and curve C represents the actually measured value of sensitivity using a ferrite head (Mn-Zn system ferrite) for recording and reproduction.
The difference between measured sentivity values, resulting from the use of different kinds of heads, is due to the differences in the maximum magnetic flux density. (Bm) and in the physical characteristics inherent in the different materials. Table I below shows the magnetic and physical characteristics of various magnetic head materials.
TABLE 1 __________________________________________________________________________ MAGNETIC AND PHYSICAL CHARACTERISTICS OF MAGNETIC HEAD MATERIALS ALLOY MATERIAL FERRITE* Conven- high Single Hot Hot tional Perm- Alphenol Sendust(al- density crystal press press sintered alloy (Alperm) pheceil) ferrite ferrite ferrite ferrite ferrite Unit __________________________________________________________________________ Ni 79 Al 16 Al 5.5 NiO 11 MnO 23 MnO 15 NiO 18.9 NiO 19 Composition Mo 4 Fe 84 Si 10.0 ZnO 22 ZnO 7 ZnO 15 ZnO 13.6 ZnO 13.5 Wt % Fe 17 Fe 84.5 Fe.sub.2 O.sub.3 67 Fe.sub.2 O .sub.3 70 Fe.sub.2 O.sub.3 70 Fe.sub.2 O.sub.3 Fe.sub.2 O.sub.3 67.5 DC 20,000 3,000 30,000 850 2,000 2,000 250 200 .mu.o 4MH.sub.z 40.uparw. 30.uparw. 60.uparw. 550 1,100* 800 250 200 Bm 8,700 18,000 11,000 3,900 4,500 4,000 4,000 2,500 gauss Hc 0.05 0.04 0.05 0.4 0.1 0.1 1 1.5 Oe Specific resistance 55.times.10.sup.-6 140.times.10.sup.-6 80.times.10.sup.-6 107 &gt;1 &gt;102 &gt;106 107 .OMEGA..cm Curie 460 400 500 125 230 150 350 250 .degree. C temperature Vicker' 132 350 500 600 600 650 750 400 hardness Density 8.72 6.5 8.8 5.3 5.1 5.1 5.3 4.5 g/cm.sup.3 __________________________________________________________________________ .uparw.Sample ring thickness 0.2 mm *(110) face ring
In video recorders using a combination system magnetic head apparatus the head assembly is often designed with an efficient reproducing system as the main criteria. Consequently, magnetic heads composed of a ferrite system magnetic material are widely used because they provide a high conversion efficiency due to their high permeability, .mu.o. However, their coercive force is high and their maximum magnetic flux density. is low, resulting in an inability to achieve high density recording. On the other hand, when the magnetic head composed of an alloy system magnetic material is used, high density recording can be achieved but reproduction occurs at a low conversion efficiency because of the low permeability .mu.o. Consequently there is a distinct disadvantage if the same head is used for recording and reproducing.
In recorders having an individual system magnetic head apparatus the recording system magnetic head apparatus is composed of an alloy system magnetic material and the reproducing system magnetic head apparatus is composed of a ferrite system mangetic material. The recording and reproducing of heads are not mounted on the same mechanism as rigidly with respect to each other. Heretofore, such individual systems have been very complicated, and thus expensive, due to the requirement for precision in video magnetic recording because of the separate mounting. The information tracks must be precisely positioned such that the recording and reproducing head mechanisms place their respective heads in the identical positions relative to the information tracks. This has only been accomplished by complicated adjustment mechanisms.